Beyond3D is currently looking into the Splinter Cell benchmark that they (B3D) created.

To cut to the chase, there's a sequence where a Pixel shader is supposed to be applied to the ocean surface...and interestingly enough, this doesn't seem to be happening all the time with the 5900.

Furthermore, the thing that's fueling the speculation at this point...beyond the fact that we now know that nVidia is a proven benchmark cheater...is the fact that they have been tipped off that an nVidia engineer's main mission in life was to focus on Splinter Cell benchmarking.